I am seeing the same thing on mine but I am getting what I think is the fan clutch staying on all the time when towing 2000 pounds. temp is creeping over 200 with 28K miles.

 

Yes, derate at 230.

 

I just finished a coast to coast 5VR pulling tour in all sorts of weather and at all posted & NOT posted speeds. The highest I saw the needle move while towing and A/C running in 98 degree temps going uphill @70mph was about 210.
I would not worry about the temps unless your tranny temps get up also. The real time to worry about it is in traffic when you can't get enough air flow accross the radiator

 

My heat gage needle runs slightly below the 200 mark when not pulling my 28' fifth wheel...when pulling the trailer, it runs just above the 200 mark.